Initial oxidation stages of hydrogen- and styrene-terminated Si(100) surfaces: A molecular dynamics study
BN Jariwala and CV Ciobanu and S Agarwal, SURFACE SCIENCE, 605, L61-L66 (2011).
We have studied the initial oxidation of H- and styrene-terminated Si(100)-2 x 1 films in O-2 atmosphere at 500 K using molecular dynamics (MD) simulations based on a reactive force field. Our simulations show that for both surface terminations the primary reactions observed are the dissociation of the oxygen molecules and the simultaneous insertion of atomic oxygen in the Si Si back-bonds. On the H:Si(100)-2 x 1 surface, another reaction is the formation of isolated Si OH bonds via the insertion of an oxygen atom in a Si - H bond. Detailed analysis of MD configurations shows that different vibrational modes of the surface Si - H and the tilting of Si dimers at 500 K facilitate the breaking of the O-2 molecule and the oxygen attack at backbonds. The combination of these reactions leads to increased amorphization of the surface as the oxidation proceeds. In the case of styrene-terminated Si(100)-2 x 1, the rate of O-2 attack was much lower than on H-terminated surface and O-atom insertions were not observed in back-bonds of Si - C bonds. In addition to lesser number of Si - H sites on styrene-Si(100)-2 x 1, another significant reason for the lower rate of O-2 attack was the repulsion of oxygen molecules resulting from the movement of phenyl rings in styrene at 500 K. (C) 2011 Elsevier B.V. All rights reserved.
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